St. Louis instead was assessed a minor penalty for delay of game for the failed challenge, and David Pastrnak scored on the power play 41 seconds into the second period to make it 4-0. Boston scored the four goals in a span of five shots.
"I think they've got to make that challenge. It was close," Blues center Ryan O'Reilly said. "It's unfortunate it puts us on the PK and they get one again right off the bat, so it kind of took the wind right out [of us]."
Ivan Barbashev got St. Louis within 4-1 at 11:05 of the second, but Krug scored on a power play 1:07 later to give Boston a 5-1 lead. Binnington was pulled after that goal.
Colton Parayko scored a power-play goal at 5:24 of the third period to make it 5-2. Noel Acciari scored an empty-net goal to make it 6-2 at 18:12, and Marcus Johansson scored at 18:35 on a power play to make it 7-2.
Binnington is 5-2 with a .937 save percentage (10 goals on 153 shots) and 1.84 goals-against average in games after a loss in the Stanley Cup Playoffs, including Game 2.
"It's the Stanley Cup Final, lots to play for," he said. "You prepare the same way. Believe in your teammates and believe in yourself. Got to do your job. You just have to handle adversity. It's not going to be perfect. These things will happen. You regroup and move on."